Propeller fan and air conditioner equipped with same

ABSTRACT

A propeller fan includes a blade. The blade has a shape in which a peak outlet angle at a trailing edge thereof exists in an outer region of the blade that is located radially outer than the representative square mean radius position, and an another peak outlet angle at a trailing edge thereof exists in an inner region of the blade that is located radially inner than the representative square mean radius position.

TECHNICAL FIELD

The present invention relates to a propeller fan and an air conditionerincluding the same.

BACKGROUND ART

Conventionally, there are known propeller fans for use in an airconditioner and the like. Rotation of the propeller fan generatesairflow (leakage flow) in the vicinity of an outer peripheral portion ofa blade, the airflow passing from a pressure surface side of the bladewhere pressure is high to a suction surface side of the blade wherepressure is low. The airflow causes vortex flows (wing tip vortexes) inthe vicinity of the outer peripheral portion of the blade. Such a wingtip vortex is liable to cause noise.

In a propeller fan of Patent Literature 1, an outer peripheral portionof a blade is provided with a bent portion for stabilizing a wing tipvortex, thereby attempting to reduce noise.

However, sufficient noise reduction effect is not always obtained bymerely providing a bent portion in an outer peripheral portion of ablade as in Patent Literature 1.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Translation of PCT InternationalApplication Publication (Tokuhyo) No. 2003-072948

SUMMARY OF INVENTION

The present invention aims to provide a propeller fan capable ofreducing noise.

A propeller fan of the present invention includes a blade. The blade hasa shape in which a peak outlet angle at a trailing edge thereof existsin an outer region of the blade that is located radially outer than therepresentative square mean radius position, and an another peak outletangle at a trailing edge thereof exists in an inner region of the bladethat is located radially inner than the representative square meanradius position.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view showing a general structure of an outdoorunit of an air conditioner according to an embodiment of the presentinvention.

FIG. 2 is a front view of a propeller fan according to a firstembodiment of the present invention.

FIG. 3 is a graph showing a relationship between radii and outlet anglesat a trailing edge in each of propeller fans.

FIG. 4A is a front view of a blade of the propeller fan according to thefirst embodiment showing five radius lines A1 to A5 which correspond tothe five radii A1 to A5 shown in the graph of FIG. 3. FIG. 4B is a frontview of a blade of a propeller fan of a reference example showing fiveradius lines A1 to A5 which correspond to the five radii A1 to A5 shownin the graph of FIG. 3.

FIG. 5 is a diagram for explaining a representative square mean radiusposition of the propeller fans.

FIG. 6 is a circumferential sectional view of the blade.

FIGS. 7A and 7B are sectional views taken along the line VIIA-VIIA inFIG. 4A. FIG. 7C is a sectional view taken along the line VIIC-VIIC inFIG. 4B.

FIG. 8A is a perspective view showing airflow in the propeller fanaccording to the first embodiment. FIG. 8B is a schematic viewillustrating the airflow.

FIG. 9A is a perspective view showing airflow in the propeller fan ofthe reference example. FIG. 9B is a schematic view illustrating theairflow.

FIGS. 10A and 10B are graphs each comparing a property of the propellerfan according to the first embodiment with a corresponding property ofthe propeller fan of the reference example. FIG. 10A shows arelationship between air quantities and blowing loudnesses. FIG. 10Bshows a relationship between air quantities and fan motor inputs.

FIG. 11A is a front view showing a part of a propeller fan according toa second embodiment of the present invention. FIG. 11B is a sectionalview taken along the line XIB-XIB in FIG. 11A.

DESCRIPTION OF EMBODIMENTS

Overall Structure of Air Conditioner

Hereinafter, a propeller fan according to an embodiment of the presentinvention and an air conditioner including the same will be describedwith reference to the accompanying drawings. FIG. 1 is a sectional viewshowing a general structure of an outdoor unit 1 of an air conditioneraccording to an embodiment of the present invention. The air conditionerincludes the outdoor unit 1 shown in FIG. 1 and an unillustrated indoorunit. The outdoor unit 1 includes an outdoor heat exchanger 3, apropeller fan 4, a motor 5 and an unillustrated compressor, which areplaced in a casing 2. The indoor unit includes unillustrated expansionmechanism and indoor heat exchanger, for example. The compressor, theoutdoor heat exchanger 3, the expansion mechanism, the indoor heatexchanger, and an unillustrated refrigerant pipe connecting thesecomponents constitute a refrigerant circuit of the air conditioner.

In the outdoor unit 1 shown in FIG. 1, the outdoor heat exchanger 3 isprovided at the back surface side of the casing 2, and a discharge port7 is provided at the front surface side of the casing 2. However, theinvention is not limited to this configuration. For example, in theoutdoor unit 1, the discharge port 7 may be provided in a top portion ofthe casing 2. The discharge port 7 is provided with a fan guard 7 a inthe form of a grill.

The propeller fan 4 is located inside the discharge port 7 of the casing2. The propeller fan 4 is connected to a shaft 5 a of the motor 5, andis driven to rotate around a rotation axis A0 by the motor 5. In thepresent embodiment, the rotation axis A0 of the propeller fan 4 lies ina forward-backward direction (horizontal direction). However, theinvention is not limited to this configuration. The rotation axis A0 maylie in a direction oblique to the horizontal direction, for example.Alternatively, in the case where the discharge port 7 is provided in thetop portion of the casing 2 in the outdoor unit 1, for example, therotation axis A0 of the propeller fan 4 may lie in a top-bottomdirection (vertical direction).

In the casing 2, a bell mouth 6 surrounding the outer circumference ofthe propeller fan 4 is provided. The bell mouth 6 is disposed between aregion X (suction region X) that lies upstream of the propeller fan 4 ina direction of airflow and a region Y (discharge region Y) that liesdownstream of the propeller fan 4 in the airflow direction. The bellmouth 6 is in the form of a ring and extends around the propeller fan 4for guiding air that has passed through the outdoor heat exchanger 3 tothe discharge port 7. The bell mouth 6 is slightly spaced from thepropeller fan 4 so as not to be in contact with the propeller fan 4.

The propeller fan 4, the motor 5, and the bell mouth 6 constitute anaxial flow blower 8. Rotation of the propeller fan 4 driven by the motor5 of the axial flow blower 8 generates a pressure difference between thesuction region X and the discharge region Y, which generates airflowpassing from the suction region X to the discharge region Y.

First Embodiment

FIG. 2 is a front view of a propeller fan 4 according to a firstembodiment of the present invention. The propeller fan 4 includes a hub11 and a plurality of blades 12. In the present embodiment, thepropeller fan 4 includes three blades 12. However, the invention is notlimited to this configuration, and the propeller fan 4 may alternativelyinclude two blades 12 or four or more blades 12. In the presentembodiment, the hub 11 and the plurality of blades 12 are integrallymolded. However, the invention is not limited to this configuration, anda plurality of components may be individually molded and then bondedtogether to form the propeller fan 4.

The hub 11 is generally in the form of a cylinder, a truncated cone orthe like, but is not limited to these shapes. The hub 11 has an outercircumferential surface 11 a joining the plurality of blades 12. Theplurality of blades 12 are disposed at regular intervals along the outercircumferential surface 11 a of the hub 11. In the case where the hub 11is in the form of a cylinder, for example, the hub 11 has asubstantially uniform outer diameter. However, in the case where the hub11 is in the form of a truncated cone, for example, the outer diameterthereof increases or decreases toward the rotation axis A0. Further, thehub 11 may be in the form of a combination of a cylinder and a truncatedcone, for example, or may have another shape. The rotation axis A0 ofthe propeller fan 4 lies at the center of the hub 11.

Each of the blades 12 includes an inner peripheral portion 13 located atradially inner side (hub 11 side) and connected to the hub 11, a leadingedge 14 located at front side in a rotational direction D, a trailingedge 15 located at rear side in the rotational direction D (reverse sidein the rotational direction D), and an outer peripheral portion 16located at radially outer side. The blade 12 has a twisted shape inwhich the leading edge 14 is totally located at the side of the suctionregion X in comparison with the trailing edge 15. Further, the blade 12has a pressure surface 21 located at the side of the discharge port 7(the side of the discharge region Y), and a negative pressure surface 22(see FIG. 6) located at the opposite side of the pressure surface 21(the side of the suction region X).

As shown in FIG. 2, the outer peripheral portion 16 includes a bentportion 17 at which an end of the blade 12 is bent on the suctionsurface 22 (toward the suction region X), and an outer peripheral edge18 defining a radially outer edge of the blade 12. The outer peripheralportion 16 has a width extending from the bent portion 17 to the outerperipheral edge 18. The bent portion 17 makes it possible to preventvortexes from occurring in the vicinity of the outer peripheral portion16 of the blade 12.

The bent portion 17 extends from the leading edge 14 (or the vicinity ofthe leading edge 14) to the trailing edge 15. In the present embodiment,the width of the outer peripheral portion 16 (distance between the bentportion 17 and the outer peripheral edge 18) increases toward thetrailing edge 15. However, the invention is not limited to thisconfiguration. Further, the bent portion 17 may be omitted, in whichcase, the outer peripheral portion 16 is defined by the outer peripheraledge 18.

Outlet Angles of Trailing Edge

Now, outlet angles θ at the trailing edge 15, which is a feature of thepropeller fan 4 of the first embodiment, will be described. In the graphshown in FIG. 3, the solid line indicates a relationship between radiiand outlet angles θ at the trailing edge 15 of the propeller fan 4 ofthe first embodiment shown in FIGS. 2 and 4A, and the broken lineindicates a relationship between radii and outlet angles θ at a trailingedge 115 of a propeller fan 104 of a reference example shown in FIG. 4B.

The propeller fan 104 of the reference example will be brieflydescribed. The propeller fan 104 of the reference example includes a hub111 and three blades 112. Each of the blades 112 includes an innerperipheral portion 113, a leading edge 114, a trailing edge 115, and anouter peripheral portion 116 (a bent portion 117 and an outer peripheraledge 118). Further, the blade 112 has a pressure surface 121 and anegative pressure surface 122 (see FIG. 7C).

As shown in FIG. 3, at the trailing edge 15 of the blade 12 of thepropeller fan 4 of the first embodiment, a plurality of peak outletangles 0 exist. Specifically, two peak outlet angles θ exist at thetrailing edge 15 of the blade 12. One of the peak outlet angle at thetrailing edge 15 exists in the outer region 12 that is located radiallyouter than the representative square mean radius position. The other ofthe peak outlet angle at the trailing edge 15 exists in the inner region12A that is located radially inner than the representative square meanradius position.

It should be noted that, in the present embodiment, the peak does notnecessarily refer to a maximum value of the outlet angles. Specifically,in such a graph as shown in FIG. 3, all of the outlet anglescorresponding to the vertices of a polygonal part convexed upward arepeak outlet angles. Therefore, one blade 12 may have a plurality of peakoutlet angles that are different from one another at the trailing edge15.

In contrast, the blade 12 of the reference example shown in FIG. 4B hasonly one peak outlet angle θ at the trailing edge 15. The peak outletangle θ is disposed at the trailing edge 115 in an outer region of theblade 112 which is located radially outer than the representative squaremean radius position Rr. The blade 112 of the reference example hasprogressively greater outlet angles θ from the inner peripheral portion113 toward the outer peripheral portion 116 at the trailing edge 115,the peak outlet angle θ being disposed in the outer region locatedradially outer than the representative square mean radius position (at aposition close to the outer peripheral portion 116).

The representative square mean radius position Rr bisects a flow area ofthe propeller fan 4 (104) into a central side portion (hub side portion)and an outer peripheral side portion. FIG. 5 is a diagram for explainingthe representative square mean radius position Rr of the propeller fan 4(104). The representative square mean radius position Rr is calculatedby the following formula (1) wherein “R” represents a representativeradius of the blade 12 (112) and “r” represents a representative radiusof the hub 11 (111).

representative square mean radius position Rr=((R ² +r ²)/2)^(0.5)   (1)

The representative radius R of the blade is calculated as follows.

In the case where the outer diameter of the blade is uniform along therotation axis, the representative radius R of the blade is equal to ahalf of the outer diameter.

In the case where the outer diameter of the blade is not uniform alongthe rotation axis, the representative radius R of the blade iscalculated as follows. The representative radius R of the blade is equalto the mean value of a minimum blade radius R1 and a maximum bladeradius R2 (R=(R1+R2)/2).

The representative radius r of the hub is, in the case where the outerdiameter of the hub is uniform along the rotation axis, equal to a halfof the outer diameter.

In the case where the outer diameter of the hub is not uniform along therotation axis, for example, in the case of the hub being in the form ofa truncated cone, the representative radius r of the hub is calculatedas follows.

The representative radius r of the hub is equal to the mean value of aminimum hub radius r1 and a maximum hub radius r2 (r=(r1+r2)/2).

Five radii A1 to A5 shown in FIG. 3 correspond to radius lines A1 to A5shown in FIGS. 4A and 4B. For example, the radius line A1 is on theblade 12 (112) and a part of a circle having the radius A1 and centeredon the rotation axis A0, in a front view of the propeller fan, as shownin FIGS. 4A and 4B. The same description is applicable to the radiuslines A2 to A5, and is therefore omitted.

In the first embodiment and the reference example shown in FIGS. 4A and4B, the radius line A3 lies on the representative square mean radiusposition Rr. However, the invention is not limited to thisconfiguration. The radius line A3 bears an outlet angle θ3 having aminimum value between the two peak outlet angles. The radius lines A1and A2 are located in the inner region 12A that is located at the sideof the hub 11 than radius line A3. The radius lines A4 and A5 arelocated in the outer region 12B that is located at the side of the outerperipheral portion 16 than radius line A3.

FIG. 6 is a circumferential sectional view of the blade 12 (for example,a sectional view taken along the radius line A3 shown in FIG. 4). In thesectional view shown in FIG. 6, an outlet angle θ at the trailing edge15 is defined by an angle between a tangent line L3 contacting to thepressure surface 21 at the trailing edge 15 and a straight line L4perpendicularly intersecting the rotation axis A0 of the propeller fan4.

In the first embodiment, as shown in FIG. 3, the peak outlet angle θ inthe inner region 12A, in other words, the outlet angle θ having amaximum value in the inner region 12A, is an outlet angle θ2 at theradius A2 (first peak position). The peak outlet angle θ in the outerregion 12B, in other words, the outlet angle having a maximum value inthe outer region 12B, is an outlet angle θ4 at the radius A4 (secondpeak position).

The outlet angle θ3 at the radius A3 is smaller than the outlet anglesθ2 and θ4. In the present embodiment, the outlet angle θ having aminimum value between the two peak outlet angles (between the radius A2and the radius A4) is the outlet angle θ3 at the representative squaremean radius position Rr (radius A3). However, the invention is notlimited to this configuration. The outlet angle θ having a minimum valuebetween the two peak outlet angles may be located at a position shiftedfrom the representative square mean radius position Rr.

In the present embodiment, the outlet angles θ progressively increasefrom the inner peripheral portion 13 to the radius A2 and progressivelydecrease from the radius A4 to the outer peripheral portion 16 (bentportion 17) at the trailing edge 15. Further, the outlet angles θprogressively decrease from the radius A2 to the radius A3 andprogressively increase from the radius A3 to the radius A4 at thetrailing edge 15. In other words, the outlet angles θ at the trailingedge 15 change in a substantially M-shaped curve as shown in FIG. 3.

A specific example of differences between the outlet angles θ2 and θ4 atthe peak radii and the outlet angle θ3 located therebetween and having aminimum value is provided as follows. The difference between the outletangle θ2 and the outlet angle θ3 may be set to fall within the rangefrom 0.5 to 10 degrees or the range from 1 to 5 degrees, for example.The difference between the outlet angle θ4 and the outlet angle θ3 maybe set to fall within the range from 0.5 to 10 degrees or the range from1 to 5 degrees, for example.

The embodiment shown in FIG. 3 shows an example in which the outletangle θ2 at the radius A2 (first peak position) and the outlet angle θ4at the radius A4 (second peak position) have the same value. However,the invention is not limited to this configuration. The outlet angles θ2and θ4 may have different values. Specifically, the outlet angle θ2 maybe greater or smaller than the outlet angle θ4.

Radii of Curvature of Pressure Surface

Now radii of curvature of the pressure surface 21, which is anotherfeature of the propeller fan 4 of the first embodiment will bedescribed. FIGS. 7A and 7B are sectional views taken along the lineVIIA-VIIA in FIG. 4A. FIGS. 7A and 7B are sectional views obtained bycutting the propeller fan 4 of the first embodiment at a plane includingthe rotation axis A0. FIG. 7C is a sectional view taken along the lineVIIC-VIIC in FIG. 4B. FIG. 7C is a sectional view obtained by cuttingthe propeller fan 104 of the reference example at a plane including therotation axis A0.

As shown in FIG. 7A, in the propeller fan 4 of the first embodiment, apressure surface 21A in the inner region 12A (inner pressure surface21A) has a concave curve surface, and a pressure surface 21B in theouter region 12B (outer pressure surface 21B) has an another concavecurve surface. hi the present embodiment, the outer pressure surface 21Bis located at the region between the representative square mean radiusposition Rr and the bent portion 17 of the outer peripheral portion 16.

The concave curve surface of the inner pressure surface 21A and theconcave curve surface of the outer pressure surface 21B adjoin eachother via the representative square mean radius position Rr. In otherwords, the concave curve surface of the inner pressure surface 21A andthe concave curve surface of the outer pressure surface 21B areadjacently disposed to each other in a radial direction. As shown inFIG. 7A, a pressure surface 21C of the specific region that bears therepresentative square mean radius position Rr lying on the boundarybetween the adjoining two concave curve surfaces and the vicinitythereof is in the form of a convex curve surface.

The concave curve surface of the inner pressure surface 21Acircumferentially extends from the leading edge 14 to the trailing edge15 and, similarly, the concave curve surface of the outer pressuresurface 21B circumferentially extends from the leading edge 14 to thetrailing edge 15.

The inner pressure surface 21A may be entirely in the form of a concavecurve surface, but is not limited to this shape. In the presentembodiment, the inner pressure surface 21A has a concave curve surfacein a region close to the representative square mean radius position Rr,but has a flat or substantially flat surface in a region close to theinner peripheral portion 13. The outer pressure surface 21B may beentirely in the form of a concave curve surface, but is not limited tothis shape. In the present embodiment, the outer pressure surface 21B issubstantially entirely in the form of a concave curve surface.

The negative pressure surface 22 extends along the pressure surface 21in such a manner that the thickness of the blade 12 does not change muchover the entire blade. Therefore, the negative pressure surface 22 has aconvex curve surface on the opposite side of the concave curve surfaceof the pressure surface 21.

The inner pressure surface 21A has a maximum radius of curvature greaterthan a maximum radius of curvature of the outer pressure surface 21B.Further, the inner region 12A includes a negative pressure surface 22A(inner negative pressure surface 22A) having a maximum radius ofcurvature greater than a maximum radius of curvature of a negativepressure surface 22B (outer negative pressure surface 22B) of the outerregion 12B. In other words, the inner pressure surface 21A is flatterthan the outer pressure surface 21B. The flat shape of the innerpressure surface 21A can also be described as follows.

In the sectional view shown in FIG. 7B, an imaginary straight line L5 isdrawn from an end T1 of the pressure surface 21, the end joining theinner peripheral portion 13 to an intersection T2 of the pressuresurface 21 with the characteristic root mean square radius line Rr. Inaddition, an imaginary straight line L6 is drawn from an end T3 of thepressure surface 21, the end joining the outer peripheral portion 16(the bent portion 17 in the present embodiment) to the intersection T2of the pressure surface 21 with the representative square mean radiusposition Rr. In the first embodiment, a maximum value D1 in the varieddistances between the imaginary straight line L5 and the pressuresurface 21 (inner pressure surface 21A) is smaller than a maximum valueD2 in the varied distances between the imaginary straight line L6 andthe pressure surface 21 (outer pressure surface 21B).

In the sectional view shown in FIG. 7B, the position that bears themaximum value D1 over the pressure surface 21 is disposed at a positioncloser to the intersection T2 than the end T1. In other words, theposition that bears the maximum value D1 over the pressure surface 21 isdisposed on the inner pressure surface 21A at a position closer to therepresentative square mean radius position Rr than the inner peripheralportion 13. In other words, in the blade 12, a portion that lies in theinner region 12A and is closer to the inner peripheral portion 13 isflatter (more planar) than a portion that lies in the inner region 12Aand is closer to the outer peripheral portion 16 (representative squaremean radius position Rr).

In contrast, in the propeller fan of the reference example shown in FIG.7C, the pressure surface 121 of the blade 112 has a single large convexsurface extending from the inner peripheral portion 113 to the bend 117of the outer peripheral portion 116. The suction surface 122 on theopposite side of the pressure surface 121 has a shape corresponding tothe pressure surface 121. In other words, the suction surface 122 has asingle large convex surface extending from the inner peripheral portion113 to the bend 117 of the outer peripheral portion 116.

As shown in FIG. 7C, the blade 112 of the reference example extendsradially, and is curved more greatly in the direction of the rotationaxis AO than the blade 12 of the first embodiment, thereby having asolid shape. Specifically, in the sectional view shown in FIG. 7C, animaginary straight line L11 is drawn from an end T11 of the pressuresurface 121, the end joining the inner peripheral portion 113 to an endT12 of the pressure surface 121, the end joining the outer peripheralportion 116 (the bent portion 117 in this reference example). In thiscase, a maximum value D11 in the varied distances between the imaginarystraight line L11 and the pressure surface 121 is considerably greaterthan the maximum values D1 and D2 in the first embodiment.

Therefore, in the reference example, each of the blades 112 has a largesectional area and, therefore, the entire propeller fan has large volumeand weight compared to the first embodiment. Accordingly, the propellerfan of the reference example has problems in terms of resource saving,cost reduction, and the like.

Further, because the blade 112 of the reference example has a solidshape as described, it is liable to elastically deform due to a stressgenerated by rotation of the propeller fan. In other words, the blade112 of the reference example has a solid shape and includes many causingpoints of elastic deformation, and is therefore liable to elasticallydeform in a deformation mode in which the blade 112 is liable toelastically deform into a planar shape (deformation mode in which theblade 112 is liable to expand radially outward) during rotation.Accordingly, the blade 112 of the reference example requiresreinforcement for preventing the elastic deformation, which results in aproblem of an increased weight.

On the other hand, the propeller fan 4 of the first embodiment shown inFIGS. 7A and 7B includes, not a single large concave curve surface as inthe reference example, but the combination of at least two concave curvesurfaces as described above. As shown in FIG. 7B, in the firstembodiment, each of the two concave curve surfaces has a peak depth (themaximum values D1 and D2). The depths D1 and D2 (maximum values D1 andD2) of the two concave curve surfaces of the first embodiment aresmaller than the depth (maximum value D11) of the concave curve surfaceof the reference example. Further, the radial length of each of theconcave curve surfaces of the first embodiment is smaller than theradial length of the concave curve surface of the reference example.

The blade 12 of the first embodiment having the above-described featuresis flatter (more planar) than the blade 112 of the reference example.The blade 12 of the first embodiment having such shape is allowed tohave, in the case of having a thickness distribution from the innerperipheral portion 13 to the outer peripheral portion 16 similar to thatof the blade 112 of the reference example, a smaller sectional area thanthe blade 112 of the reference example. This allows each of the blades12 to have a small weight and, therefore, allows the entire propellerfan 4 to have a small volume and weight compared to the referenceexample.

Further, because the blade 12 of the first embodiment is flatter thanthe blade 112 of the reference example, it is unlikely to elasticallydeform due to a stress generated by rotation of the propeller fan 4. Inother words, since the blade 12 of the first embodiment usually has aplanar shape, the amount of an elastic deformation is small.

Further, in the present embodiment shown in FIG. 7A, the momentum of theair flowing along the pressure surface 21 locally changes greatly in theouter pressure surface 21B as shown by arrows in the figure. Incontrast, in the reference example shown in FIG. 7C, the momentum of theair flowing along the pressure surface 121 changes over the entirepressure surface 121 as shown by arrows in the figure.

Recessed portion of Trailing Edge

Now a recessed portion 19 of the trailing edge 15, which is furtheranother feature of the propeller fan 4 of the first embodiment will bedescribed. As shown in FIG. 4A, the recessed portion 19 is provided onthe trailing edge 15 of the blade 12 of the first embodiment, therecessed portion being oriented toward the leading edge 14. The recessedportion 19 is provided in a region bearing the representative squaremean radius position Rr. The recessed portion 19 is not an essentialconstituent and may be omitted. The recessed portion 19 has asubstantially V-shape or a substantially U-shape in a front view, forexample, but is not limited to these shapes.

The provision of the recessed portion 19 at the representative squaremean radius position Rr on the trailing edge 15 where the pressure isliable to increase on the pressure surface 21 makes it possible toreduce a pressure rise at the representative square mean radius positionRr on the trailing edge 15. This allows the air flowing along thepressure surface 21 from the leading edge 14 toward the trailing edge 15to move toward the hub 11 and to the outer peripheral portion 16 in sucha manner as to avoid the representative square mean radius position Rrin the vicinity of the trailing edge 15. Therefore, the effect ofguiding airflow in a circumferential direction can be enhanced. Theeffect of guiding airflow in the circumferential direction can befurther enhanced by the combination of this effect of guiding airflow inthe circumferential direction provided by the recessed portion 19, andthe guiding effect provided by disposing the respective peak outletangles θ in the hub 11-side region and the outer peripheral portion 16side-region, the regions being on opposite sides of the representativesquare mean radius position Rr.

Further, in the present embodiment, a bottom 19 a of the recessedportion 19 (leading part of the recessed portion 19 in the rotationaldirection D) lies at the representative square mean radius position Rr.However, the invention is not limited to this configuration. In the casewhere the bottom 19 a of the recessed portion 19 lies at therepresentative square mean radius position Rr, the above-describedguiding effect can be further enhanced.

Airflow during Rotation

Now airflow generated during rotation of the propeller fan 4 of thefirst embodiment will be described in comparison with the referenceexample. FIG. 8A is a perspective view showing airflow in the propellerfan according to the first embodiment, and FIG. 8B being a schematicview illustrating the airflow. FIG. 9A is a perspective view showingairflow in the propeller fan of the reference example, and FIG. 9B beinga schematic view illustrating the airflow.

As shown in FIGS. 8A and 8B, in the propeller fan 4 of the firstembodiment, the effect of guiding airflow in the circumferentialdirection is high especially in the inner region 12A. This restrains airfrom flowing to the outer peripheral portion 16.

In contrast, in the reference example shown in FIGS. 9A and 9B, there isa low effect of guiding airflow in a circumferential direction in theinner region. Therefore, air is liable to flow to the outer peripheralportion 116.

Consequently, blowing loudness is considerably lower in the firstembodiment than in the reference example, as shown in FIG. 10A.Furthermore, the first embodiment makes it possible to, while reducingblowing loudness, obtain an equal air quantity by a substantially equalfan motor input to those of the reference example as shown in FIG. 10B.In the first embodiment, reduction in weight is achieved withoutsacrificing blowing performance.

Second Embodiment

FIG. 11A is a front view showing a part of a propeller fan 4 accordingto a second embodiment of the present invention, and FIG. 11B being asectional view taken along the line XIB-XIB in FIG. 11A.

The propeller fan 4 of the second embodiment differs from the firstembodiment in that each of blades 12 has a solid shape similarly to theblade 112 of the reference example. Specifically, the blade 12 of thesecond embodiment includes, as shown in FIG. 11B, a pressure surface 21including a single large concave curve surface extending from an innerperipheral portion 13 to a bent portion 17 of an outer peripheralportion 16.

However, the second embodiment differs from the reference example inthat the blade 12 has outlet angles θ having the same features as thoseof the first embodiment shown in, for example, FIG. 3. Specifically, inthe second embodiment, the blade 12 has a shape in which a peak outletangle θ at the trailing edge 15 thereof exists in the outer region 12Bof the blade 12 that is located radially outer than the representativesquare mean radius position Rr, and an another peak outlet angle θ atthe trailing edge 15 thereof exists in an inner region 12A of the blade12 that is located radially inner than the representative square meanradius position Rr.

Summary of Embodiments

As described above, in the first embodiment and the second embodiment,the representative square mean radius position Rr serves as a referenceat which the flow area of the propeller fan 4 is bisected into theradially inner region and the radially outer region, and each of theouter region 12B occupying one half of the flow area and the innerregion 12A occupying the remaining half of the flow area is providedwith the function of guiding air in the circumferential direction,thereby making it possible to effectively achieve the noise reduction.

Specifically, in these embodiments, the shape of the blade in which apeak outlet angle θ at the trailing edge 15 exists in the outer region12B is adopted, to thereby obtain a large amount of work of the fan atthe trailing edge 15 of the outer region 12B. This can enhance theeffect of guiding air flowing along the pressure surface 21 of the outerregion 12B in the circumferential direction. Further, in theseembodiments, the shape of the blade in which an another peak outletangle θ at the trailing edge 15 exists in the inner region 12A isadopted, to thereby obtain a large amount of work of the fan also at thetrailing edge 15 of in the inner region 12A. This can also enhance theeffect of guiding air flowing along the pressure surface 21 of the innerregion 12A in the circumferential direction. Therefore, it is possibleto prevent air from flowing to the outer peripheral portion 16 (wingtip), and an increase in airflow (leakage flow) passing from thepressure surface 21 to the negative pressure surface 22 in the vicinityof the outer peripheral portion 16 is suppressed. Consequently, theoccurrence of wing tip vortexes caused by leakage flow can be prevented,which makes it possible to achieve the noise reduction. Further, theprevention of an increase in leakage flow can also prevent degradationof blowing performance.

In the first embodiment, the inner region 12A includes the pressuresurface 21 having a maximum radius of curvature greater than a maximumradius of curvature of the pressure surface 21 of the outer region 12B.In other words, in the first embodiment, the inner region 12A has asmaller maximum value of curvature radius and is therefore flatter thanthe outer region 12B. Therefore, the blade 12 is allowed to have a smallcross-sectional area especially in the inner region 12A. This allows theblade 12 to be light in weight and small in volume.

In the first embodiment, the pressure surface 21 of the inner region 12Aand the pressure surface 21 of the outer region 12B include a concavecurve surface. In the first embodiment, because the pressure surface 21of the inner region 12A and the pressure surface 21 of the outer region12B each include a concave curve surface, it is possible to enhance, ineach of the regions, the effect of guiding air flowing along thepressure surface 21 in the circumferential direction.

Furthermore, in the first embodiment, the pressure surface 21 of theouter region 12B has a maximum radius of curvature smaller than amaximum radius of curvature of the pressure surface 21 of the innerregion 12A, and the respective pressure surfaces of the regions 12A and12B each have a concave curve surface. Because changes in the pressureover the pressure surface 21 and the negative pressure surface 22 isgreat in the outer region 12B close to the outer peripheral portion 16,the radius of curvature in the outer region 12B is set to a small value,to thereby make it possible to enhance the effect of guiding air flowingalong the pressure surface 21 of the outer region 12B in thecircumferential direction. Consequently, the entire pressure surface 21is further unlikely to cause the leakage flow.

In the first embodiment, the inner region 12A and the outer region 12Beach have single concave curve surface and single peak outlet angle.Such relatively simple structure allows the blade 12 to be light inweight and small in volume while achieving the noise reduction.

In the first embodiment and the second embodiment, the trailing edge 15of the blade 12 includes the recessed portion 19 in the region bearingthe representative square mean radius position Rr, the recessed portionbeing oriented toward the leading edge 14. In these embodiments, therecessed portion 19 is provided in the region of the trailing edge 15bearing the representative square mean radius position Rr where thepressure rise is otherwise liable to be greatest. Therefore, thepressure rise can be reduced in the vicinity of the recessed portion 19.This allows the air flowing from the leading edge 14 toward the trailingedge 15 to move toward the hub 11 and to the outer peripheral portion 16in such a manner as to avoid the representative square mean radiusposition Rr in the vicinity of the trailing edge 15. This can enhancethe effect of guiding airflow in the circumferential direction.

Further, in the blade 12 of the first embodiment, as clear from thepositional relationship between an auxiliary line L1 and positions P1and P2 shown in FIG. 2, the position P1 where the leading edge 14 andthe outer peripheral portion 16 join each other is located furtherforward in the rotational direction D than the position P2 where theleading edge 14 and the inner peripheral portion 13 join each other.

Further, in the blade 12 of the first embodiment, as clear from thepositional relationship between an auxiliary line L2 and positions P3and P4 shown in FIG. 2, the position P3 where the trailing edge 15 andthe outer peripheral portion 16 join each other is located furtherrearward in the rotational direction D than the position P4 where thetrailing edge 15 and the inner peripheral portion 13 join each other.

In contrast, in the blade 112 of the propeller fan of the referenceexample shown in FIG. 4B, as clear from the positional relationshipbetween an auxiliary line L12 and positions P13 and P14, the positionP13 where the trailing edge 115 and the outer peripheral portion 116join each other is located further forward in the rotational direction Dthan the position P14 where the trailing edge 115 and the innerperipheral portion 113 join each other.

Therefore, in the first embodiment shown in FIG. 2, the blade 12 is madeto be compact especially in the inner region 12A and is thereby light inweight, compared to the reference example shown in FIG. 4B.

Modifications

Although the embodiments of the present invention have been described,the present invention is not limited to these embodiments. Variouschanges and modifications may be made without departing from the spiritof the invention.

The above-described embodiment illustrates the case where the propellerfan is used in the outdoor unit 1 of the air conditioner. However, theinvention is not limited to this application. The propeller fan may beused, for example, as a fan for an indoor unit of an air conditioner oras a ventilation fan.

The first embodiment illustrates the case where the pressure surface 21Aof the inner region 12A and the pressure surface 21B of the outer region12B each have a concave curve surface. However, the invention is notlimited to this configuration. For example, the pressure surface 21A ofthe inner region 12A may be in the form of a flat surface, while thepressure surface of the outer region 12B may be in the form of a curvedsurface (concave curve surface or convex curve surface). Alternatively,the pressure surface 21A of the inner region 12A may be in the form of acurved surface (concave curve surface or convex curve surface), whilethe pressure surface of the outer region 12B may be in the form of aflat surface.

The above-described embodiments are summarized as follows.

A propeller fan of the present invention includes a blade, and the bladehas a shape in which a peak outlet angle at a trailing edge thereofexists in an outer region of the blade that is located radially outerthan the representative square mean radius position, and an another peakoutlet angle at a trailing edge thereof exists in an inner region of theblade that is located radially inner than the representative square meanradius position.

In this configuration, the representative square mean radius positionserves as a reference at which a flow area of the propeller fan isbisected into the radially inner region and the radially outer region,and each of the outer region occupying one half of the flow area and theinner region occupying the remaining half of the flow area is providedwith a function of guiding air in a circumferential direction, therebymaking it possible to effectively achieve noise reduction, specificallyas follows.

Generally, air flowing along the pressure surface is liable to flow tothe outer peripheral portion (wing tip) due to a pressure gradient, acentrifugal force and the like during rotation of the propeller fan.

Accordingly, in this configuration, the shape of the blade in which apeak outlet angle θ at the trailing edge exists in the outer region isadopted, to thereby obtain a large amount of work of the fan at thetrailing edge of the outer region. This can enhance the effect ofguiding air flowing along the pressure surface of the outer region inthe circumferential direction. Further, in this configuration, the shapeof the blade in which an another peak outlet angle θ at the trailingedge exists in the inner region is adopted, to thereby obtain a largeamount of work of the fan also at the trailing edge of the inner region.This can also enhance the effect of guiding air flowing along thepressure surface of the inner region in the circumferential direction.Therefore, it is possible to prevent air flowing to the outer peripheralportion (wing tip), and an increase in airflow (leakage flow) passingfrom the pressure surface to the negative pressure surface in thevicinity of the outer peripheral portion is suppressed. Consequently,the occurrence of wing tip vortexes caused by leakage flow can beprevented, which makes it possible to achieve noise reduction. Further,the prevention of an increase in leakage flow can also preventdegradation of blowing performance.

Further, as described above, in the propeller fan including theabove-described configuration, air flowing onto the pressure surface ofthe blade from the leading edge is prevented from moving radiallyoutward to the outer peripheral portion (wing tip), so that the airdominantly flows in the circumferential direction. This allows the hubto have a small height (thickness of the hub along the rotation axisAO), which allows the propeller fan to be light in weight, specificallyas follows.

In the propeller fan, if the hub is made to have a small height, theblade will also need to have a small blade height in the innerperipheral portion thereof that joins the outer circumferential surfaceof the hub (at a joint where the blade joins the hub). The blade heightrefers to the difference in height (difference in height along therotation axis) between one end (the leading edge end) and the other end(the trailing edge end) of a camber line on the joint. If the blade hasa small height, the amount of work (head rise) of the blade is small inthe vicinity of the joint, so that the air flowing onto the pressuresurface from the leading edge is liable to move radially outward to thewing tip where the amount of work is large (the wing tip where the headrise is great). Therefore, if the hub is made to have a small height inthe conventional propeller fan, it will be difficult to allow air toflow dominantly in the circumferential direction. In order to obtain alarge amount of work (head rise) of the blade in the vicinity of thejoint, it is appreciated to widen the blade extending in the form of afan from the joint to the wing tip, in other words, lengthen a cordlength in the vicinity of the joint, to thereby enlarge the area(increase the integrated value) of the pressure surface in the vicinityof the joint. However, this will increase the weight of the blade, whichmakes it difficult to provide a propeller fan that is light in weight.

On the other hand, in the propeller fan of the present invention, theblade having the shape in which a peak outlet angle at the trailing edgeexists in the outer region and an another peak outlet angle at thetrailing edge exists in the inner region is adopted, which allows air toflow dominantly in the circumferential direction, as described above.Therefore, the propeller fan of the present invention is allowed toinclude the hub having a smaller height than the conventional fan and isthereby light in weight, while allowing air to flow dominantly in thecircumferential direction.

In the propeller fan of the present invention, the peak outlet angle inthe outer region and the peak outlet angle in the inner region may havethe same or different values. In the case of having different values,the peak outlet angle in the outer region may have a greater or smallervalue than the peak outlet angle in the inner region.

(2) In the propeller fan of the present invention, it is preferable thatthe inner region include a pressure surface having a maximum radius ofcurvature greater than a maximum radius of curvature of a pressuresurface of the outer region.

In this configuration, because the inner region has a smaller maximumradius of curvature and is therefore flatter than the outer region, theblade is allowed to have a small cross-sectional area especially in theinner region. This allows the blade to be light in weight and small involume.

(3) In the propeller fan of the present invention, it is preferable thatthe pressure surface of the inner region and the pressure surface of theouter region each include a concave curve surface.

In this configuration, because the pressure surface of the inner regionand the pressure surface of the outer region each include a concavecurve surface, it is possible to enhance, in each of the regions, theeffect of guiding air flowing along the pressure surface in thecircumferential direction.

Furthermore, the following effect can be obtained by including both ofthe above-mentioned configurations (2) and (3). In this case, thepressure surface of the outer region has a maximum radius of curvaturesmaller than a maximum radius of curvature of the pressure surface ofthe inner region, and the respective pressure surfaces of the regionseach have a concave curve surface. Because changes in the pressure overthe pressure surface and the negative pressure surface is great in theouter region close to the outer peripheral portion, the radius ofcurvature in the outer region is set to a small value, to thereby makeit possible to enhance the effect of guiding air flowing along thepressure surface of the outer region in the circumferential direction.Consequently, the entire pressure surface is further unlikely to causethe leakage flow.

(4) It is possible to provide, as an example, an embodiment of thepropeller fan of the present invention wherein the inner region and theouter region each have single concave curve surface and single peakoutlet angle.

(5) In the propeller fan of the present invention, it is preferable thatthe trailing edge of the blade have a recessed portion recessed toward aleading edge of the blade in a region including the representativesquare mean radius position.

In this configuration, the recessed portion is provided in the region ofthe trailing edge including the representative square mean radiusposition where the pressure rise is otherwise liable to be greatest.Therefore, the pressure rise can be reduced in the vicinity of therecessed portion. This allows the air flowing from the leading edgetoward the trailing edge to move toward the hub and to the outerperipheral portion side in such a manner as to avoid the representativesquare mean radius position. This can enhance the effect of guidingairflow in the circumferential direction.

(6) An air conditioner of the present invention includes theabove-mentioned propeller fan. Therefore, noise is reduced in this airconditioner.

REFERENCE SIGNS LIST

1 outdoor unit

2 casing

3 outdoor heat exchanger

4 propeller fan

5 motor

6 bell mouth

7 discharge port

8 axial flow blower

11 hub

12 blade

12A inner region

12B outer region

13 inner peripheral portion

14 leading edge

15 trailing edge

16 outer peripheral portion

17 bent portion

18 outer peripheral edge

19 recessed portion

19 a bottom

21 pressure surface

21A inner pressure surface

21B outer pressure surface

22 negative pressure surface

A0 rotation axis

D rotational direction

Rr representative square mean radius position

θ outlet angle

1. A propeller fan comprising a blade, wherein the blade has a shape inwhich a peak outlet angle at a trailing edge thereof exists in an outerregion of the blade that is located radially outer than therepresentative square mean radius position, and an another peak outletangle at a trailing edge thereof exists in an inner region of the bladethat is located radially inner than the representative square meanradius position, the inner region includes a pressure surface having amaximum radius of curvature greater than a maximum radius of curvatureof a pressure surface of the outer region.
 2. (canceled)
 3. A propellerfan according to claim 1, wherein the pressure surface of the innerregion and the pressure surface of the outer region each include aconcave curve surface.
 4. A propeller fan according to claim 1, whereinthe inner region and the outer region each have single concave curvesurface and single peak outlet angle.
 5. A propeller fan according toclaim 1, wherein the trailing edge of the blade has a recessed portionrecessed toward a leading edge of the blade in a region including therepresentative square mean radius position.
 6. An air conditionercomprising a propeller fan according to claim 1.